Inductance system



Nov. "13, 1934. A. GEBHARD INDUCTANCE SYSTEM 2 Sheets-Sheet l INVENTOR. Qua/664w,

' Original Filed Dec. 22 1928 a I W M ATTORNEY INDUCTANCE SYSTEM Original Filed Dec. 22, 1928 2 Sheets-Sheet 2 ATTORNEY A.

Reissued Nov. 13, 1934.

, UNITED STATES PATENT OFFICE Wired Radio, Inc., New

ration of Delaware York, N. Y., a corpo- Original No. 1,753,408, dated April 8, 1930, Serial No. 327,988, December 22, 1928. Reissue No. 18,070, dated May 19, 1931, Serial No. 522,709,

March 24, 1931.

Application for reissue January 15, 1932, Serial No. 586,926

16 Claims.

My invention relates to inductance systems in general and more specifically to inductance systems employed in thermionic tube transmitters.

An object of my invention is to provide an I. inductance system for high frequency transmitters of the type employing thermionic tubes having the anodes thereof cooled by a circulatory liquid.

Another object of my invention is to provide an inductance system wherein the high frequency output circuit includes the circulatory system of the cooling fluid.

, Stillanother object of my invention is to provide an inductance system wherein the cooling 1 fluid circulates through the high frequency inductance of an electrically balanced thermionic tube transmitting system.

A further object of my invention is to'provide an inductance system including a fluid-cooled portion and an auxiliary portion adapted to be connected in circuit therewith with means for electrically coupling a load to the fluid cooled portion or to the auxiliary portion.

A still further object of my invention is to 25 provide an inductance system including a fluid cooled dual passage tubular member having means for defining the radio frequency potential of the electrical center thereof including a radio frequency path to ground through a condenser. A better understanding of the inductance system ofmy invention can be had by referring to the specification following and to the accompany-' ing drawings wherein:

Figure 1 is a diagrammatic illustration show- 'ing the inductance system of my invention and Fig. 2 is a schematic circuit diagram showing the inductance system of my invention.

In transmitting, systems employing thermionic tubes having their anodes cooled by a circulatory liquid it is essential to efdciency that the losses of high" frequency energy in the cooling system be reduced to a minimum. With the connec tion of the cooling fluid to and from the thermionic tubes by means of an insulated length of tubing or hose, considerable loss of energy occurs. This is due primarily to the high potential of high frequency energy concentrated at the points of connection. The inductance system of my invention reduces these losses to a minimum and in addition provides many advantages, as will appear from the specification following:

Hg. 1 of the accompanying drawings is a diagrammatic illustration showing the inductance v system of my invention. Thermioni'c tubes 1 and N .3 are of the type adapted to have the anodes thereof cooled by a circulatory liquid. Tubes 1 and 2 are contained in receptacles or sockets 3 and 4 respectively. The cooling liquid is assoelated with thermionic tubes 1 and 2 by means of helical coil 5. Coil -5 comprises a. length of metal having dual passage for'conveying the cooling fluid to and from the respective tubes. Coil 5 is herein illustrated as comprising individual lengths of metal tubing which are placed parallel to each other and positioned in this manner by welding or other suitable means. This pro.

vides a single electrical conductor and a 'dual' passage for the circulating liquid. The circulating liquid is associated with coil 5 by means of connectors 5 and 5 which conduct the liquid to and from the source of supply. Coil 5 is so designed that the frequency characteristics of the inductance thereof combined with the capacity of condenser 8 provides approximately the lowest frequency at which it is desired to operate the transmitter. The high frequency energy may be transferred to another circuit by inductance 13 which may be positioned in inductive relation to said coil 5 and electrically associated with the load circuit 14. Load circuit 14 may comprise a space radio radiating system, a wired radio system or additional thermionic tube amplifier cir.

hen it is desired to operate the transmitter on a'fr'equency higher than that obtained by employing coil 5 and capacity 8 alone, an auxiliary inductance 111 is connected in parallel with coil 5 and capacity 8. This is accomplished by closing switch members 9 and 10. Should coil 5 and inductance 11 have like frequency characteristics the resultant frequency characteristics when the two are connected in multiple would be the sum of the two. Thus suppose the frequency characteristics of coil 5 and capacity 8 were such as to give an oscillation constant of and that L was 10 and C was 5. Assuming that the frequency characteristics of inductance 11 were such as when employed with a capacity having a value of 5 would likewise give an oscillation constant of 50'. If then inductance 11 is connected in parallel relation with coil 5 the resultant value of L would be 5 and the oscillation constant 25. A decrease in the oscillation constant is in effect an increase in the frequency characteristics of the circuit, as is well known in the art. It is further obvious that any frequency characteristics may be had by employing the well known ele'- able source of alternating current.

mentary law for parallel inductances which formula is identical with that employed for parallel connection of resistances.

Fig.2 is a schematic circuitdiagram-showing the inductance system of my invention employed in a representative amplifier circuit arrangement...

Like reference characters are employed in this illustration. The anode circuits of thermionic tubes 1 and 2 are energized from-source 16. Capacity 28 is connected to the mid-connection of coil 5 and to ground b The capacity or condenser 28 is not the ordinary by-pass condenser used across a high voltage direct current source such as generator 16.

- fluid.

but is a condenser especially located with respect to the geometrical center of the coil .5 so as to. provide alow impedance path to ground from the fluid inlet and discharge connections of the-- coil. The condenser 28 is located immediately adjacent the inductance coil 5 and one side' of the condenser is connected to the mid-point connection and the other sideconnected to ground 12 The connection of the condenser 28 to ground l2 provides a low impedance path for radio. frequency currents and serves to establish a nodal point on the coil at the point where. the liquid is introduced and discharged. In this way a low voltage condition exists at the point of admission and discharge of the fluid and the electrical center of the coil is fixed. The radio frequency potential at the electrical center of the coil is a minimum and admission or discharge of the cooling fluid may be effected with minimum losses. Inductance 11 is associated with space radio radiating system 12--1 2 by coil 12. Coil 13 is provided by which connections to a suitable load circuit may be had when different adjustments of frequency are not properly related to the frequency characteristics of circuit 12. 12,- 12 Coil 13 is inductively coupled with the fluid cooled inductance 5 and connected to any suitable load circuit such as a wired. radio circuit or.

an antenna ground circuit connected to the loads 14. If however the auxiliary inductance 11 is connected through switches 9 and 10 and tuned by means of condenser 8 across the fluid cooled inductance .5, the radio frequency coupling may be established through coupling 'coil 12 .to the, antenna ground system 12 -12", in which event the coupling coil 13 would be disconnected and not used. The cathode circuits of thermionic tubesl and 2 are energized from transformer 22 the latter of which is associated with any suit- Capacities 23 are provided as by-paths for high frequency energy to ground 12'. A source of control electrode biasing potential 17 supplies the proper potential to the respective control electrodes to insure the desired operational characteristics.

Thermionic tubes 1 and 2 are connected in an electrically balanced circuit arrangement, induce tance 18 and capacity 2'7 constituting the input circuits and inductances 5-9 and capacity 8 constituting the output circuits. The circuits are electrically balanced by balancing condensers 20 and 21 which provide means for ,counterbalanc-' ingor neutralizing unlike characteristics ofthe circuits.

densers 25 and 26. Capacity 24 is provided-to offer a by-path to the high frequency energy and exclude the same from source 17. Different :adjustments in the frequency characteristics are The input circuit of thermionic tubes -1 and 2 are associated-with any suitable source of high frequency energy 19 by means of con-.

obtained by opening or closing switch members 9 and 10.

Coil 5 comprises any suitable metal tubing and the inherent frequency characteri'stics'of the inductance which'it constitutes arenot easily adjusted. Since the opposite ends of the coil are connected to the sockets of the thermionic tubes and a circulatory cooling liquid is flowing therethrough,it is obvious that it would be impractical to attempt to vary the length of the tubing. In

the inductance system of my invention the frequency characteristics of the circuit including coil 5 may be easily adjusted to any desired value without-disturbingthe circulation of the cooling The advantages arising from the use of my invention will. be appreciated when it is considered as thefiuid inlet and discharge connections are,

located at the geometrical center of. the inductance the shift of theelectrical center awayfrom the geometrical center" moves the high frequency voltage node away from the geometrical center, thereby introducing-a definite radio frequency potential at the fluid inlet and discharge :con nections. As a. result this. radio. frequencypotential is imposedacross the hose coil connection.

resulting in losses which decrease the efliciency' of the transmitter. Ordinarily the electrical center of the inductance'may float to either side of the geometrical center of the inductance. and

there is no means for establishing the electrical center of thehelix at the fluid inlet and" discharge connections. Ordinarily there is no method for defining the potential of the electrical'center ofv the inductance so that the electricalcen'ter may be maintained at 'substanti 11y zero. radio frequency potential. V 1

Experiencehas shown that quite a. high voltagebuilds up at the geometrical center of the coil if this geometric center is not established asthe electrical center by use of a low impedance path to ground. In one case during some tests conducted on a circuit inwhich the geometric cen-.. ter of the coilidid not havea low impedance path to ground,'the cooling fluid. connections which consisted of rubber hose actually burned off. The amount of loss in the system to 'causethis effect was obviously considerable. V t

In practice there are differences in-internal capacitiesof tubes and stray capacities in theradio transmitter. There must be certain tolerances to which tubes are manufactured. They cannot bemade exact. This is also true for the. construction of the two' br anches of the circuit of the radio transmitten. In a transmitter it is necessary to have controls for'changing the tuning and balance condensers. These controls are arranged to be operated from the. front panel of the transmitter and the mechanism connected between the electrical element and-the control on the front panel is generallyby way of an in-.

sulated member which has a certain amount. of 1 capacity "although smalL. elementimay nct exist onsthe 1 othenhalfwoftha system:.md.as a re"? sult axsmall unbalance of-the oaimoity exists inl the circuit-.-. inequality in therloadszdrawniby the twollialvesrof the-.1011? cuitl.

My'invention-avoids all of the disadvantages hcreinbeforerreoitedhy preeiselyrfixingthe electrical center of theinductanodcoil at'-the'ge0i.- metrical center thereof, that.is,= at the lnlet. and discharge connections:v ofrthez coolingrfluidz My: invention furthers advantages". for by securing an electricala center at the geometric center thcloads-on: theindividuai-tubes arcymore. closely equalized: thus: permitting: the use of. the tubes uptomaximum power output. By allow-- ing" the electrical. center: to: float, as heretofore, the loads are-not at. alletimes equal: and there-- fore: one branch of.- the circuit will be: liable to. be loaded. more than: the other bronchi-of. the; circuit which will prevent the: use" of "the: tubes @up: to maximum. poweroutput.

A still: further: improvement in: the: useon? the. of my" invention is that when using caze pacity' coupling" to: an asymmetrical load: circuit, the: establishment of ther electricalycentert at the; geometric center prevents wide differencesin the loadingrofl the twdbranchesof. the circuit. Even. when: coupled toa: symmetrical load; the establishment-oft the electrical center of. the: coil; atithe geometric center prevents. differences in the cur- I rents-in the" twdbranches' of. the load.- circuit.

Ancther advantage of the: system= of my; invention is that the balance of the system is im-- proved; The balance referrcd'toinrthis instance is that controlled by condensers and. 2r and: which is necessary to prevent coupling between input and output circuitawhich: would render the: circuit inoperative; The'accuracy-of. this balance maybe improved by the useof: a low impedance path to ground; thus improving: the: stability ofthe system as-a whole.

- It is" this radio frequency path to ground; positively included in circuit: the midpoint ofthe water cooled inductance which. enables theeiectrical-center ofthe'watercooled inductance-to be established and shifting of the electrical centel. with respect to the" geometrical: center prevented; Differences" in' capacityexisting. in: the tubes and in the different branches: of the: push-- pull-l amplifier system m the circuit, arrangement my invention will not shift the electrical. canter to either side' of geometrical center and. therefore the" electrical center will be maintained at substantially zero radio frequency potential. preventing the passage of substantial radio frequency energy over the: hose connections at. the fluid inlet and discharge points and thereby in.- creasing the: eflicie'ncy cf the transmitter.

I realize that many modifications of. in-- ductance system of my inventionv arepossible: 'without departing from; the ofmy invention. Any suitable type of thermionic tubes may be employed and any number of such tubes may 'be connected in suitable circuit arrangements "j'Similar inductances may be employed in the in- ,put circuit when a liquid cooled inductance is necessary or so desired. It is to be understood "that my invention shall not be restricted to precisely the arrangements shown in the accompagnying drawings or described in the foregoing specification but only as defined by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows: 1. An inductance system comprising a helix,

said.helixlrcomprising;adouble passage for cool ing fluid and a common passage for electrical energy, a cooling: fluid inlet and; discharge connection. along said helix and? meansincludinga radio frequency path to ground from a point along." said; helix. for establishing the electrical center-of said. helix atsaid fluid inlet and discharge connections.

2. An inductance system comprising a. helix, saidzhelix. comprising aldual passage conductor for'coolingfluid, a common passage for electrical energy, means for establishing a high frequency voltage node atthe electrical center of said helix for'reducing tliehigh frequencyvoltage to a minimumat said electrical center of said helix including? a .radio'. frequency path to ground: and 1 aconnecting. member provided at the electrical center of" said helix. for admitting and discharging: cooling: fluid;

3; A high. frequency inductance system comprising: a. helical formation of metallic tubing.

means for associating a cooling fluid with said" tubing at the electrical center of the inductance, andan electrical. circuit connected to said. tubing. at. a. point intermediate the ends thereof, said" circuit including aradio frequency path to ground for. maintaining said tubing at alow radio fre-c quency potential at the point of connection. of said; circuit thereto and defining the electrical: center thereof.

'4. An inductance system. comprising in com-.

bination almetallic member of helical form pro-I vidlng a double passage for the circulation of? liquid, a; load circuit inductively coupledwith said."

metallic member, a pathto ground, having low.

impedance toradio frequency-currents, said path,

being connected with-said metallic member interf 5'. In an inductance system the combinationof:

a helix, said'helixcomprising metal tubing having a; double passage for the circulation of a cooling fluid, means provided: at the electrical center of 'said helix for admitting said fluid to said; pas..- sages, and a path to ground through a condenser connected to the electrical center ofsaid helix for maintaining the radi'o'frequency potential at the point of admission of the cooling fluid to the passages in said helix at a minimum.

6; An inductance system comprising in combi nation a plurality-of lengths of metal tubing immediately adjacent to each other comprising a single electrical conductor and comprising'a plurality of conductors for the circulation of a liquid, and a path to ground having a low radio frequency impedance connected to said lengths of metal tubing intermediate the ends thereof for fixing, the electrical center of said tubing and maintaining the radiov frequency potential at. the. point of admission and discharge of the liquid to the conductors at a, minimum.

7. An inductance coil comprising a. helical formation of metallic tubing providing a plurality of individual fluid conducting passages immediately adjacent to each other and constituting a single electrical conductor, fluid inlet and discharge connections for said tubing intermediate the ends of said coil, an electrical circuit connected between said fluid inlet and discharge connections and the ground, said circuit including a low impedance path to radio frequency currents and operating to maintain the electrical center of said metallic tubing at minimum radio frequency potential.

8. An inductance coil comprising a helical formation of metallic tubing having a plurality of individual fluid conducting passages and a single electrical passage, a path to ground extending between the metallic tubing at a point intermediate the ends thereof and a low radio frequency impedance in said path for defining the electrical center of said coil, and fluid connecting members associated with said coil at theelectrical center thereof.

9. An inductance system comprising in combination a metallic member of helical form providing a double passage for the circulation'of cooling fluid, a load circuit, means for inductive 1y coupling said load circuit with said helical'metallic member, means for defining the potential of the electrical center of said inductance including a radio frequency path to ground, and means for admitting and discharging cooling fluid at the electrical center of said inductance.

10. An inductance system comprising a metallic member of helical form providing a double passage for the circulation of cooling fluid, a load circuit, an inductance coil adapted to be electrically connected in parallel with said metallic member, means for conjointly tuning said metallic member and. said inductance, a radio frequency path to ground connected to said metallic member intermediate the ends thereof for establishing the electrical center of said metallic member, fluid inlet and discharge connections for said metallic'member at said electrical center,'and independent means inductively coupled to said metallic member and to said inductance for symmetrically transferring energy from said metallic member to said load circuit.

11. A high frequency inductance system comprising in combination a metallic member of ;jointlytuning said inductance and said member,

separate means-inductively coupled to said member and to said inductance and adapted-to be electrically connected with. said load circuit,

means including a radio frequency path to ground.

culation of cooling fluid, a load circuit, an inductance conductively connected with said metallic member, means for conjointly tuning said inductance and said member, separate means inductively coupled to said member and to said inductance and adapted to be electrically connected with said load circuit, a low impedance at a point intermediate theends thereof, said circuit including a condenser connected on one side thereof to ground and forming a radio-frequency path to groundfor maintaining said tubing at a low radio frequency potential at the point of connection of said circuit thereto and defining the electrical center thereof.

14. An inductance system comprising in com bination a metallic member of helical form providing a'double passage for the circulation of coolingfluid, a load circuit, means for inductively coupling said load circuit with said helical me-- tallic member, and a condenser connected to ground at one side' and connected with said metallic member at the" fluid inlet and discharge connectionthereof at the other side, said condens'er providing a radio frequency'path' to ground for defining the potential of the electrical 'center of: said inductance at the fluid inlet and discharge connection thereto.

15. An inductance system comprising in com-' bination a metallic member of helical form providing a-double passage for the circulation of liq-- uid, a load circuit inductively coupled with said metallic member, a condenser having low imped ancetof'radio frequency currents, said condenser being connected at one side of said metallic mem-' ber intermediate the ends thereof and being connected at the other'side to ground and operating to define the electrical center of said xmetallic member, and' fluid inlet and discharge connections forsaid metallic member at the electrical centerthereof;

16. An-inductan'ce system comprising in combination a metallic tubing wound in.a helix and forming a pair-of conductors for the admission of a fluid and constituting a single electricalco'ndenser, fluid inlet and discharge connections at the-electrical center ofsaid inductance, a condenser having a low radio frequency impedance connected at one side to said fluid inlet and discharge' connectio'ns and connected at the other side to ground, the electrical path provided by said condenser operating to fix the electrical'-center of said tubing coincident, with said fluid inletand discharge connections and maintain the radio frequency potential atthe point of admission and discharge of the fluid at a minimum.

LOUIS .A. GEBHARD. 

